Bradykinin (BK) is a peptide composed of nine amino acids (Arg.sup.1 -Pro.sup.2 -Pro.sup.3 -Gly.sup.4 -Phe.sup.5 -Ser.sup.6 -Pro.sup.7 -Phe.sup.8 -Arg.sup.9, SEQ ID NO:1) which, along with lysyl-BK (kallidin), is released from precursor kininogens by proteases termed kallikreins. Plasma kallikrein circulates as an inactive zymogen from which active kallikrein is released by Hageman factor. Tissue kallikrein appears to be located predominantly on the outer surface of epithelial cell membranes at sites thought to be involved in transcellular electrolyte transport.
Two major kinin precursor proteins, high molecular weight and low molecular weight kininogen, are synthesized in the liver, circulate in plasma, and are found in secretions such as urine and nasal fluid. High molecular weight kininogen is cleaved by plasma kallikrein, yielding BK, or by tissue kallikrein, yielding kallidin. Low molecular weight kininogen, however, is a substrate only for tissue kallikrein. In addition, some conversion of kallidin to BK may occur inasmuch as the amino terminal lysine residue of kallidin is removed by plasma aminopeptidases. Plasma half-lives for kinins are approximately 15 sec., with a single passage through the pulmonary vascular bed resulting in 80-90% destruction. The principle catabolic enzyme in vascular beds is the dipeptidyl carboxypeptidase kininase II or angiotensin-converting enzyme (ACE). A slower acting enzyme, kininase I, or carboxypeptidase N, which removes the carboxyl terminal Arg, circulates in plasma in great abundance. This suggests that it may be the more important catabolic enzyme physiologically. Des-Arg.sup.9 -bradykinin as well as des-Arg.sup.10 -kallidin formed by kininase I acting on BK or kallidin, respectively, are active as BK.sub.1 receptor agonists, but are relatively inactive at the more abundant BK.sub.2 receptor at which both BK and kallidin are potent agonists.
Bradykinin is known to be one of the most potent naturally occurring stimulators of C-fiber afferents mediating pain. It also is a potent vasodilator, edema-producing agent, and stimulator of various vascular and nonvascular smooth muscles in tissues such as uterus, gut and bronchiole. The kinin/kininogen activation pathway has also been described as playing a pivotal role in a variety of physiologic and pathophysiologic processes, being one of the first systems to be activated in the inflammatory response and one of the most potent stimulators of: (i) phospholipase A.sub.2 and, hence, the generation of prostaglandins and leukotrienes; and (ii) phospholipase C and thus, the release of inositol phosphates and diacylglycerol. These effects are mediated predominantly via activation of BK receptors of the BK.sub.2 type.
Direct application of bradykinin to denuded skin or intra-arterial or visceral injection results in the sensation of pain in animals and in man. Kinin-like materials have been isolated from inflammatory sites produced by a variety of stimuli. In addition, bradykinin receptors have been localized to nociceptive peripheral nerve pathways and BK has been demonstrated to stimulate central fibers mediating pain sensation. Bradykinin has also been shown to be capable of causing hyperalgesia in animal models of pain. (See, Burch et al, "Bradykinin Receptor Antagonists", J. Med. Chem., 30:237-269 (1990) and Clark, W. G. "Kinins and the Peripheral and Central Nervous Systems", Handbook of Experimental Pharmacology, Vol. XXV: Bradykinin, kallidin, and kallikrein. Erdo, E. G. (ed.), 311-322 (1979)).
These observations have led to considerable attention being focused on the use of BK antagonists as analgesics. A number of studies have demonstrated that bradykinin antagonists are capable of blocking or ameliorating both pain as well as hyperalgesia in both animals and man. See, Ammons, W. S. et al, "Effects of intracardiac bradykinin on T.sub.2 -T.sub.5 medial spinothalamic cells", The American Physiological Society, 0363-6119 (1985); Clark, W. G., "Kinins and the Peripheral and Central Nervous Systems", Handbook of Experimental Pharmacology, Vol. XXV: Bradykinin, kallidin, and kallikrein. Erdo, E. G. (ed.), 311-322 (1979); Costello, A. H. et al, "Suppression of carrageenan-induced hyperalgesia, hyperthermia and edema by a bradykinin antagonist", European Journal of Pharmacology, 171:259-263 (1989); Laneuville et al, "Bradykinin analogue blocks bradykinin-induced inhibition of a spinal nociceptive reflex in the rat", European Journal of Pharmacology, 137:281-285 (1987); Steranka et al, "Antinociceptive effects of bradykinin antagonists", European Journal of Pharmacology, 16:261-262 (1987); Steranka et al, "Bradykinin as a pain mediator:Receptors are localized to sensory neurons, and antagonists have analgesic actions", Neurobiology, 85:3245-3249 (1987).
Currently accepted therapeutic approaches to analgesia have significant limitations. While mild to moderate pain can be alleviated with the use of nonsteroidal anti-inflammatory drugs and other mild analgesics, severe pain such as that accompanying surgical procedures, burns and severe trauma requires the use of narcotic analgesics. These drugs carry the limitations of abuse potential, physical and psychological dependence, altered mental status and respiratory depression which significantly limit their usefulness.
Prior efforts in the field of BK antagonists indicate that such antagonists can be useful in a variety of roles. These include use in the treatment of burns, perioperative pain, migraine and other forms of pain, shock, central nervous system injury, asthma, rhinitis, premature labor, inflammatory arthritis, inflammatory bowel disease, etc.
For example, Whalley et al, in Naunyn Schmiederberg's Arch. Pharmacol., 336:652-655 (1987) have demonstrated that BK antagonists are capable of blocking BK-induced pain in a human blister base model. This suggests that topical application of such antagonists would be capable of inhibiting pain in burned skin, e.g. in severely burned patients in whom large doses of narcotics are required over long periods of time and for the local treatment of relatively minor burns or other forms of local skin injury.
The management of perioperative pain requires the use of adequate doses of narcotic analgesics to alleviate pain while not inducing excessive respiratory depression. Post-operative narcotic-induced hypoventilation predisposes patients to collapse of segments of the lungs, a common cause of post-operative fever, and frequently delays discontinuation of mechanical ventilation. The availability of a potent non-narcotic parenteral analgesic could be a significant addition to the treatment of perioperative pain. While no currently available BK antagonist has the appropriate pharmacodynamic profile to be used for the management of chronic pain, frequent dosing and continuous infusions are already commonly used by anesthesiologists and surgeons in the management of perioperative pain.
Several lines of evidence suggest that the kallikrein/kinin pathway may be involved in the initiation or amplification of vascular reactivity and sterile inflammation in migraine. (See, Back et al, "Determination of components of the kallikrein-kinin system in the cerebrospinal fluid of patients with various diseases", Res. Clin. Stud. Headaches, 3:219-226 (1972)). Because of the limited success of both prophylactic and non-narcotic therapeutic regimens for migraine as well as the potential for narcotic dependence in these patients, the use of BK antagonists offers a highly desirable alternative approach to the therapy of migraine.
Bradykinin is produced during tissue injury and can be found in coronary sinus blood after experimental occlusion of the coronary arteries. In addition, when directly injected into the peritoneal cavity, BK produces a visceral type of pain. (See, Ness et al, "Visceral pain: a review of experimental studies", Pain, 41:167-234 (1990)). While multiple other mediators are clearly involved in the production of pain and hyperalgesia in settings other than those described above, it is also believed that antagonists of BK have a place in the alleviation of such forms of pain as well.
Shock related to bacterial infections is a major health problem. It is estimated that 400,000 cases of bacterial sepsis occur in the U.S. yearly; of those 200,000 progress to shock, and 50% of these patients die. Current therapy is supportive, with some suggestion in recent studies that monoclonal antibodies to Gram-negative endotoxin may have a positive effect on disease outcome. Mortality is still high, even in the face of this specific therapy, and a significant percentage of patients with sepsis are infected with Gram-positive organisms which would not be amenable to anti-endotoxin therapy.
Multiple studies have suggested a role for the kallikrein/kinin system in the production of shock associated with endotoxin. See, Aasen et al, "Plasma Kallikrein Activity and Prekallikrein Levels during Endotoxin Shock in Dogs", Eur. Surg., 10:50-62 (1977); Aasen et al, "Plasma Kallikrein-Kinin System in Septicemia", Arch. Surg., 118:343-346 (1983); Katori et al, "Evidence for the involvement of a plasma kallikrein/kinin system in the immediate hypotension produced by endotoxin in anaesthetized rats", Br. J. Pharmacol., 98:1383-1391 (1989); and Marceau et al, "Pharmacology of Kinins: Their Relevance to Tissue Injury and Inflammation", Gen. Pharmacol., 14:209-229 (1982). Recent studies using newly available BK antagonists have demonstrated in animal models that these compounds can profoundly affect the progress of endotoxic shock. (See, Weipert, et el., "Attenuation of Arterial Blood Pressure Fall in Endotoxic Shock in the Rat Using the Competitive Bradykinin Antagonist Lys-Lys-[Hyp.sup.2, Thi.sup.5.8, D-Phe.sup.7 ]-BK", Brit J. Pharm., 94, 282-284, (1988)). Less data is available regarding the role of BK and other mediators in the production of septic shock due to Gram-positive organisms. However, it appears likely that similar mechanisms are involved. Shock secondary to trauma, while frequently due to blood loss, is also accompanied by activation of the kallikrein/kinin system. (See, Haberland, "The Role of Kininogenases, Kinin Formation and Kininogenase Inhibitor in Post Traumatic shock and Related Conditions", Klinische Woochen-schrift, 56:325-331 (1978)).
Numerous studies have also demonstrated significant levels of activity of the kallikrein/kinin system in the brain. Both kallikrein and BK dilate cerebral vessels in animal models of CNS injury. (See, Ellis et al, "Inhibition of Bradykinin- and Kallikrein-Induced Cerebral Arteriolar Dilation by Specific Bradykinin Antagonist", Stroke, 18:792-795 (1987) and Kamitani et al, "Evidence for a Possible Role of the Brain Kallikrein-Kinin System in the Modulation of the Cerbral Circulation", Circ. Res., 57:545-552 (1985)) Bradykinin antagonists have also been shown to reduce cerebral edema in animals after brain trauma. Based on these data, it is believed that BK antagonists should be useful in the management of stroke and head trauma.
Other studies have demonstrated that BK receptors are present in the lung, that BK can cause bronchoconstriction in both animals and man and that a heightened sensitivity to the bronchoconstrictive effect of BK is present in asthmatics. Some studies have been able to demonstrate inhibition of both BK and allergen-induced bronchoconstriction in animal models using BK antagonists. These studies indicate a potential role for the use of BK antagonists as clinical agents in the treatment of asthma. (See, Barnes, "Inflammatory Mediator Receptors and Asthma", Am. Rev. Respir. Dis., 135:S26-S31 (1987); Burch et al, "Bradykinin Receptor Antagonists", J. Med. Chem., 30:237-269 (1990); Fuller et al, "Bradykinin-induced Bronchoconstriction in Humans", Am. Rev. Respir. Dis., 135:176-180 (1987); Jin et al, "Inhibition of bradykinin-induced bronchoconstriction in the guinea-pig by a synthetic B.sub.2 receptor antagonist", Br. J. Pharmacol., 97:598-602 (1989) and Polosa et al, "Contribution of histamine and prostanoids to bronchoconstriction provoked by inhaled bradykinin in atopic asthma", Allergy, 45:174-182 (1990)) Bradykinin has also been implicated in the production of symptoms in both allergic and viral rhinitis. These studies include the demonstration of both kallikrein and BK in nasal lavage fluids and that levels of these substances correlate well with symptoms of rhinitis. (See, Baumgarten et al, "Concentrations of Glandular Kallikrein in Human Nasal Secretions Increase During Experimentally Induced Allergic Rhinitis", J. Immunology, 137:1323-1328 (1986); Jin et al, "Inhibition of bradykinin-induced bronchoconstriction in the guinea-pig by a synthetic B.sub.2 receptor antagonist", Br. J. Pharmacol., 97:598-602 (1989) and Proud et al, "Nasal Provocation with Bradykinin induces Symptoms of Rhinitis and a Sore Throat", Am. Rev. Respir. Dis., 137:613-616 (1988)).
In addition, studies have demonstrated that BK itself can cause symptoms of rhinitis.
Stewart and Vavrek in "Chemistry of Peptide Bradykinin Antagonists", Bradykinin Antagonists: Basic and Chemical Research, R. M. Burch (Ed.), pages 51-96 (1991) discuss peptide BK antagonists and their possible use against effects of BK. A great deal of research effort has been expended towards developing such antagonists with improved properties. However, notwithstanding extensive efforts to find such improved BK antagonists, there still remains a need for more effective BK antagonists.
The two major problems with presently available BK antagonists are their low levels of potency and their extremely short durations of activity. Accordingly, important objectives of the present invention include the provision of novel BK antagonist peptides which are characterized by increased potency and duration of action. Other objectives will also be hereinafter evident.